All the power generators in the world won't do you much good if they aren't properly lubricated. Gas is a no-brainer, but engine oil can be easy to forget. It will make your generator run more smoothly, reduce wear and tear and save energy [source: Henry].
If you run a lawn mower or like to change the oil in your car, you probably already have some on hand. The amount you need for a generator depends on the size of its engine, so check your equipment's user manual. A new generator requires its first oil change within 25 hours of use, and you should refill the machine's oil supply every 50-60 hours or so [source: The Family Handyman].